The Autobots have successfully foiled the Decepticons' attempt at conquering the universe, and are now living in harmony on Earth, stockpiling energy for Cybertron in cooperation with the governments of the planet they guest. Unknown to them, however, the Decepticons have survived, turning their fallen space cruiser into an underwater base of operations. After an untold number of attempts, Shockwave -- Megatron's appointed guardian of Cybertron -- manages to communicate with the Decepticons to inform them of the increasingly precarious situation on their home planet. He has also completed the plans for a new intergalactic transport system, which involves a spacebridge that will be able to send energon cubes to Cybertron. At the end of an apparently fruitless search, Bumblebee and Spike Witwicky happen upon the spacebridge in a dried-out riverbed, but they are spotted and -- following a futile escape attempt by Bumblebee -- captured. The Decepticons keep Spike prisoner while Megatron alters Bumblebee's memory circuits to make him lead the other Autobots on a wild goose chase into a cave, where the Decepticons wait to trap them. Confident that the Autobots are out of the way, the Decepticons return to the spacebridge location to continue testing. Needing a driver to guide the transport vehicle to Cybertron, they bestow the dubious honour on Spike. But even as the vehicle races for the bridge, the Autobots, having freed themselves from the cave and restored Bumblebee's memory, arrive at the scene and rescue Spike. Megatron attempts to salvage the energon cubes and get them to Cybertron in time, but a laser blast causes one of them to explode, hurling him inside the spacebridge just before it launches. Beamed to Cybertron in one piece, he vowes ultimate revenge.